1. Field of the Invention
The present invention relates to architectural glass block panels and windows (“panels”) and methods of making such panels. More particularly, the invention relates to a glass block panel that is resistant to the shock wave effects of a blast event, for example, an explosion.
2. Background of the Invention
Glass blocks may be used instead of solid (i.e., non-transparent) materials, plate glass or other fenestration materials in the construction of walls and partitions. Aside from the aesthetic advantages that the glass blocks may provide over other solid or glass materials, the glass blocks may be preferable because they are transparent and allow light to filter through, thereby permitting viewing with desired levels of privacy through the wall, or creating a brighter room or office space.
With the increased threat and awareness of terrorist and criminal attacks from explosive ballistic devices, responsible government and commercial organizations are responding with more stringent building requirements along with better products and construction methods. In the past, the majority of injuries to building occupants have been caused by shattered glass fragments or shards sent flying through the air from the blast force.
An explosion will cause variations in air pressure, called shock waves, to radiate from the source of the blast. The actual effect of a blast is a function of its type, magnitude, duration and distance from where the blast took place. “Standoff distance” is a distance maintained between a building and the potential location of an explosive detonation, like a sidewalk or parking lot, by use of a fence and gated entry, where inspections for explosives are done. Standoff distances will be longer where there is potential to detonate a larger explosive device, like one driven in a car or truck, and shorter where the device could be carried. With a nearly infinite range of explosive devices and potential standoff distances, standards have been developed to simplify blast parameters for testing and application purposes. To that end, a blast pulse is often simplified to a triangular shape where the pressure rises from ambient pressure almost instantaneously and then declines linearly back to ambient.
The key parameters used to define a blast in standards and specifications for fenestration are:                Maximum pressure is the highest level of pressure above ambient that is typically reached immediately after detonation. Measured in psi (pounds per square inch), it is often referred to as peak pressure and applied pressure. Overpressure is often used to describe pressures above ambient.        Impulse is a function of the pressure and duration and is the area under the pressure curve from detonation to when the pressure returns to ambient. It is measured in psi-msec (pounds per square inch—milliseconds).        
The other key parameter for fenestration is how well it resists a blast in order to protect people inside of a building. The two commonly used standards defining that protection are the ASTM Hazard Rating (from ASTM International, previously American Society for Testing and Materials) and the GSA Performance Condition (from the General Services Administration).
ASTM has developed a document with designation F 1642-04 titled “Standard Test Method for Glazing and Glazing Systems Subject to Airblast Loadings.” It is used to define standard testing procedures and resulting “Hazard Rating.” GSA is a government agency that provides support to federal, state and local government agencies and to contractors and suppliers providing goods and services to them. Part of their function is to qualify suppliers and products. For blast resistant fenestration, they provide GSA Test Protocol GSA-TS01-2003 titled “US General Services Agency Test Method for Glazing and Window Systems Subject to Dynamic Overpressure Loadings.” GSA has prescribed the following Building Classifications:
GSA BuildingMaximumClassificationPressureImpulsePerformanceLevel A 0 0NALevel B 0 0NALevel C 4 psi28 psi-msec3b or betterLevel D10 psi89 psi-msec3b or betterLevel EClassifiedClassifiedper spec
Thus, there is a need for glass construction material that provides the aesthetic and visual benefits discussed above in conjunction with increased resistance to explosive blasts. Historically, most glass block installations were done with masonry, such that the glass blocks were connected to each other with mortar or mortar-like adhesives, akin to the construction of a brick wall. With the advent of improved sealants and adhesives, however, an increasing number of glass block installations have been done with silicone, either alone or in conjunction with plastic spacer systems. One advantage the better silicones can offer over traditional mortar is that the assembled glass block panel can flex, allowing it to absorb forces from powerful air pressures caused by nature or those that are man made. While natural air pressure, such as that found in hurricanes, may be on the order of 100 pounds per square foot, air pressures for blast events may be ten to twenty times larger, sometimes approaching or even exceeding 1800 pounds per square foot. The present invention seeks to provide a glass block panel that can withstand such high pressures without any glass cracking or any loss of material.
Flat glass fenestration has made good progress in blast resistance by utilizing glass lamination and framing techniques to allow a glass pane to flex, so that even when the glass cracks, the underlying laminate layer may help hold the pane together, thereby limiting the scattering of glass fragments. The invention described herein builds on the natural structure of glass block construction to allow the fenestration to flex elastically to blast pressures. The structure behaves like a flexible web of independent glass units. Whereas laminated flat glass panes often will crack and release fragments during a blast, there is no such cracking or loss of glass with the present invention. This is particularly important to people who are in the proximity of a building when a blast event occurs because they may be pushed up against the building and underneath windows where shattered glass might be raining down on them.
Accordingly, it is an object of the present invention to provide a glass block construction material that provides the aesthetic and visual benefits of an ordinary glass or glass block panel in conjunction with increased resistance to explosive blasts.